Electrical discharge treatment and machining apparatus

ABSTRACT

A method of electrical discharge machining employs a sugar mill roll as a cathode and an electrode for performing treatment serving as an anode. Water is injected therebetween and concurrently therewith repetitive transient arc discharges are effected, whereby the grooved surface of the roll is provided with satin finish. The electrode can be a turner or scraper plate which is machined with the roll serving as the tool electrode and subsequently employed with the roll as a mill.

United States Patent [72] Inventors Toshio Niwa Osaka; Yasuo Kimoto, Osaka; Katsunori Tamiya, Kobe Hisashi Okamura, Osaka, all of,

Japan 85 l ,556

[21] App]. No.

[22] Filed Aug. 20, 1969 [45] Patented Aug. 17, 1971 [73] Assignee Hitachi Shipbuilding and Engineering Co.

- Ltd.

Nishi-ku, Osaka, Japan [32] Priority Aug. 23, 1968, Aug. 23, 1968, Aug. 23,

1968, Aug. 23, 1968 [33] Japan [31] 43/60762, 43/6075), 43/60761 and [54] ELECTRICAL'DISCHARGE TREATMENT AND MACHlNlNG APPARATUS 7 Claims, 9 Drawing Figs.

[52] US. Cl 219/69 M, 219/69 D [51] Int. Cl 823p H08 [50] FieldofSearch 219/69 D,

69 E, 69 M, 69 P, 69 v I [56] References Cited UNITED STATES PATENTS 2,974,215 3/1961 lnoue 219/69 v x 3,145,286 8/1964 Fehling 6: 1.. 219 69 M 3,158,728 11/1964 Webb 219/69P 3,240,914 3/1966 11111 et al. 219/69 M 3,333,080 7/1967 DeVries 219/69 M Primary Examiner-R. F. Staubly Anorney- Dawson, Tilton, Fallon 8L Lungmus ABSTRACT: A method of electrical discharge machining employs a sugar mill roll as a cathode and an electrode for performing treatment serving as an anode. Water is injected therebetween and concurrently therewith repetitive transient arc discharges are effected, whereby the grooved surface of the roll is provided with satin finish. The electrode can be a turner or scraper plate which is machined with the roll serving as the tool electrode and subsequently employed with the roll as a mill.

ELECTRICAL-DISCHARGE TREATMENT AND MACHININGA'PPARATUS The present invention relates 'to, a :method of electrical discharge treatment andimachiningtand more particularly ma 'FIG. 7 is a diagram of a discharge circuit of capacitance type'showing a'modification of the electric circuit to be used in theelectrical discharge treatment of the present invention;

method ofelectrical discharge treatment and ma'chining tobe used in treating the surface of-a sugarmill roll,-in machining the electrode for treating the roll surface andinmachining a turner plate and a scraper'to'be'employed with the ro'll.

In extracting sugar juice 'from' sugarcane for the'manufacture of sugar, a pair of :upper'and lower rollers is employed. However, there is a drawback that the-grooves formed onthe rollsurfaces aregradually worn off by the fibers of sugarcane as if subjected to-abrasion to cause the slippage of the sugarcane and thereby impair the efficiency of sugar juicerextraction. In order to overcome-such defect,-a proposal wasmade in which several large groovesfor drawing in the sugarcane were provided in the roll surface at a predetermined langle with the above mentioned grooves, but the slippage of the sugarcane could not substantially be-eliminated by the proposed structure. 0n th e'contrary, some of the sugarcane fibers were left unsqueezeddue to the provision of the large grooves, which resultedin the deterioration'of; extractionl'efficiency to the correspondingextent. x r

An object of the present invention isto provide a method 'for'effecting satin finish treatment on the surface ofa sugar FlG.- 8 is a diagram of a discharge circuit of transistor type showing another ,modification ofthe electric circuit to be used :in theelectricaldisc'harge treatment of thepresent invention; and

FIG. is 'a curve graph representing the relationship between the discharge-current peak valuedischarge duration and theelectrode consumption rate. H

Referring to FIG. 1, 'it will be seen that sugarcane 2 is squeezedbetweena pair of upper and lower sugar mill rolls 1, andsugar juice'3 is extracted. Instead of providing tworolls l, 1,'three'rollsmay beprovided, one roll in an elevated'position and two rolls, spaced apart from each other, disposed paired. The present invention contemplates eliminating this problem.

FIGS. 2 and 3 illustrate the electrical discharge treatment of the'present invention as it is performed on the roll I. The roll 1 serves as a cathode, and a treating electrode 7 having a pormill roll which" is capable of increasingthecoeffi cient of'friction on the roll surface and imparting-corrosionand wear-resisting properties tothe surface of thezroll to therebyimprove the sugar-juice extraction efficiency.

' V 'sid'eof theroll l in facing relation therewith with a predeter- Anotherobject of the present invention to provide the 'surfaceofa sugar mill roll with satin finishiin a short period of timeand with ease. Y t

- Stillanother object of the present'invention is to'provide a I method for machining by transference-a treating electrode as well as'a turner plate and-a scraperto be'used-with-the sugar mill roll to the shape identicalwith the shape of-th'eigrooves on the roll with ease and in ashort'periodoftime.

Still another object of the. present'inven'tion istorprovide a machiningmethod for imparting; durability to=a= turner plate and a scraper to be employed-with the sugar'mill rollhw These and other objects, features and advantagesof the present invention will become apparent from-the :following description. I 7 1 .To sum up, the method ofaelectrica l discharge; treatment andirnachining of the present invention comprises employing-a sugar 'millroll as a cathode'and a treating electrode as an anode,providingwater'therelzzetween and effecting concurrently therewith repetitive transient arc dischargeswhich are unidirectional and of an'appropr'iate waveform.

The present invention will be fully understood fromthe following detailed description with reference to accompanying drawings, inwhich: j

FIG. 1 isa diagrammatic side elevation showing a pair of sugar mill rollsas sugar juice is being extracted from the'sugar cane; v v, FIG. 2 is a diagrammatic side elevation of anxapparat-us for effecting electrical discharge treatment as the surface of a sugar mill roll is being treated toprovidesatinfinishby applying the method of electrical discharge treatment in ac- .cordance'with thepresent invention;

FIG. 3 is-a plan view-showing .the electrical discharge treatment apparatusinFlG. 2; i

FlG.- 4 is an enlarged perspective view showing a treating electrode and'a water retainer in a box form;

FIG. '5 is -a fragmentary 'plan view on an enlarged scale showings satin fini'shedroll with partbroken away anda turnerplate to be machined by transference based upon the form of the roll; v I:

FIG. 6 'is'a diagram of a discharg'e circuitpf capacitance type showing an example of'the electric'circ'uit to be used in the electrical discharge treatment of the present invention;

tion'7 a-with projections and indentations in conformity with those of the roll 1 and serving as an anode is disposed at the mined gap foreffecting-discharge. Thetreating electrode 7 is housed in a water retainer8 in theshape of a box and supported on aholder'9 together with the retainer. An opening 811 o'fthewater retainer-Sfaces totherolll, and rugged'portions al'0acorresponding to the projections and indentations of the 'rolleryl-are formed along the forward edges of sidewalls 10 parallel to the axialdirection of the roll 1. Concave arcuate portions 111: in conformity with theperipheral surface of the roll lare' formed-along thefront edges of sidewalls 1"1 perpendicular'to the axial direction of the roll "1. The 'electrode ,1". .holder 9'isfixed to the end of a piston rod 13 of an oil cylinder 4 -1-2 so'thatbyoperating the oil cylinder 12 the gap between the roller-land the treating electrode 7 may be adjusted to an appropriate distance to effect electrical discharges. The oil cylinder "12- is'securedto support l5mounted on a movable support plate .l4'whose under face is provided with a fitting portion 17 in slidably fitting engagement with a rail 16 which is disposed parallel tothe axial direction of the roll 1. The rail 16 is supported at a predetermined level by a stand 20 mounted'on a'base l9for supporting the entire body of the sugarmill 18. Fixed to'the stand 20 is a'holder 22 for a brush 2] held incontact with oneend of the roll 1. A water-ejecting nozzle23 is disposed between the roll 1 and the treating electrode'7.

The roll 1 is slowly rotated in the counterclockwise direction inFlG. 2 'andat the same time, water 24 is supplied from-a nozzle 23. The'water24 is retained in the retainer 8, so that -water 24 is present between the roll 1 and the treating electrode'7all the time. In this state, electrical discharges are effected and the'roll 1 is formed with a satin-finished surface la because of the reasons to be described later. When the roll lis brought into a turn of rotation, thetreating electrode 7 is retracted by'operating the cylinder 12 so that rugged portion 7a of the electrode may not strike against the roll 1 when moved sidewise, 'and the movable support plate 14 is thereaftermoved'sidewise manually'by. a distance corresponding to *the length of the treatingelectrode' 7. After the gap carrying out this operation in succession, the entire body of the'roll 1 is provided .'with satin'finish'Although only one roll 1 is shown in'FIG. 2,;in case where the sugar mill has two or threerolls, I, the same number of treating electrodes 7 are provided to effect satin-finishing treatment concurrently on two or more rolls. y

FIG. 6 shown an embodiment of the electric circuit require for generating transient arc discharge for a short period of time which is employed in working the present invention. In this drawing, designated at 25 is a direct current power source; at 26, a resistor; at 27, a capacitance; at 28, a rectifier; and at 29, a self-inductance. The roll I acting as a cathode, treating electrode 7 serving as an anode, water-ejecting nozzle 23 and flushing water 24 shown in FIG. 2 are schematically illustrated in FIG. 6. In this electric circuit, when the insulation between the roll 1, i.e. cathode and the treating electrode 7, i.e. anode, is broken a u'nidirectioned transient arc is produced, and the self-inductance or the capacitance, if varied, causes variations in the wave form of the discharge current. A satin-finished surface having roughness of approximately 2 I-Irms. M r-in. is obtained with a capacitance of 8 p.F, and roughness of. approximately l IIrms. M a-in. is achieved with a capacitance of 200 In order to effect discharges at diffused points on the sugar mill roll surface and blow out or remove the metal at discharge points so as to improve treating effects, there is a need to provide water between the roll and the treating electrode. If no water is present between the roll and the electrode, aerial transient arc discharges take placetherebetween. With such aerial discharges, it is impossible to fulfill theintended object of the present invention to provide satin finish over the entire roll surface, because aerial discharges occur at points of low distribution on the roll surface with repetitive discharges raking place concentrically. Furthermore, since the discharge points on the roll surface which are melted by joule heat produced by arc discharge are solidified again in the case of the aerial discharges, the grooved roll surface is susceptible to deformation and there is a possibility that the increase in coefficient of friction and improvements in resistance to wear and corrosion may not be achieved as intended by the invention.

As already described, it is required that the sugar mill roll be employed as a cathode and the treating electrode as an anode. The polarity, if reversed, causes leakage current to pass between the roll and the treating electrode through an electrolyte in the water to result in deposition of a large amount of anode products on the roll, and it becomes no longer possible to effect satisfactory surface treatment. In case where an oil having high insulating property is used in place of water so as to prevent the leakage of current, there arises a hazard to cause a fire, and moreover, the use of oil is not desirable since the roll is employed for the extraction of sugar juice which is is a food. I I By carrying out electrical discharge treatment with the electric circuit shown in FIG. 6 under the following treating conditions, results given in FIG. 9 were obtained.

Voltage of DC. power source: 134v. Electrostatic capacity of capacitance: 16 pf. Resistance: 11 S2 Self-inductance: -500 pH.

Material: mild steel Tma'tmg {size: 30 mm. wide and 50 mm. long material: soft cast iron Rolldiameter: 860 mm.

in weight is not more than 95 percent and if the ais 6 A/,u.S,

the electrode consumption rate is percent. The treatment of the roll surface this being chiefly effected. Marked wear on the treating electrode is by no means desirable from the view point of carrying out economical and efficient treatment. In treating the roll surface, therefore, it is preferable to employ a discharge current which is not lower than 0.1 A/aS, especially not lower than 0.2 A/uS.

FIG. 5 illustrates the satin-finished surface of the roll obtained by subjecting it to the discharge treatment described above which was carried out with act 1 Alps. The surface of the roll 1 having grooves 6 22 mm. in depth and 32mm. in pitch is formed with a satin-finished surface of roughness of approximately 4 I-Irms. HIM-III. By examining the" state of the surface it was found to have, improved:=hardness up to the depth of 2 p.-in. from the surface. That is-to say, the result of Vickers hardness test performed under a load of 25 gr. showed that, whereas a conventional roll had I-IV of about-250, the

roll of the present invention described abovehad improved I-IV of about 750. Remarkable improvements have also been achieved with respect to coefficient of friction, and wear-resistin'g and corrosion-resisting properties. As compared with a conventional roll, the coefficient of friction and wear resistance were increased by several tens of percent. When subjected to corrosion test with 5 percent nitric acid solution, the conventional roll showed corrosion resistance represented by the reduction of about I mg./cm. 2 min whereas the example in accordance with the present invention was found to undergo a reduction of 0.1 mg./cm. min.

In case where the value of self-inductance is increased to make the value of the discharge current not higher than 0.05 A/uS by employing the electric circuit-shown in FIG. 6 The electrode consumption rate achieved is not lower'than 200 percent, resulting in wear chiefly on the treating electrode. By applying this principle it has further been found out that based upon the fonn of the grooved sugar mill roll, the tips of the treating electrode and of the scraper and turner plate which are used with the roll can be transfer formed by electrical discharge machining. Thatis to say, in case where a discharge current with the discharge current peak value (A)'/ discharge duration (as) notexcecding 0.05 is produced in the electric circuit shown in FIG. 6 while the roll is being rotated, the rate of wear on the electrode achieved becomes not less than 200 percent, consumption, namely shaping being effected chiefly on the treating electrode. For example, with a tool electrode 30 mm. in width and a roll 3,000 mm. in circumference, an electrode consumption rate of 300 percent is attained when a discharge current of 0.04 A/,u.S-is used. Suppose the density of the roll and that of the treating electrode are the same, the wear or disintegration of the roll is one three-thousandth that of the treating electrode, the treating electrode which is initially in a flat shapebeing worn off and machined to the shape identical with that of the roll grooves without causing deformation of the grooves on the roll surface. If a turner plate or a scraper whose forward end if initially linear as indicated in a chain line in FIG. 5 is placed in position as an anode in place of the treating electrode, the forward end will be machined to the shape of the roll grooves, namely to the projected or indented shape indicated in a solid line in the same drawing, just as seen in the case of the treating electrode. It will readily be understood that the surface thus machined has also been improved in hardness and durability the same as the roll surface.

The electric current shown in FIG. 7, a modification of the circuit in FIG. 6, utilizes the charging and discharging actions of a capacitance 30. In FIG. 7, numeral 31 indicates a rectifier, the other same reference numerals as in FIG. 6 designating the same constituent elements.

The electric circuit shown in FIG. 8, another modification of the circuit in FIG. 6, utilizes the switching action of a semiconductor such as a transistor 32 or thyristor. In FIG. 5, the numeral 33 indicates a pulse generator, the other reference numerals identical with those in FIG. 6 refer to the identical elements.

It will be apparent fromthe foregoing description that by theapplication of electrical discharge in water of the present invention, not only the time required for treating the surfaces of the sugar mill roll can be remarkably reduced but the durability of the roll can also be greatly improved. In addition, due to the increase in the coefficient of friction of the roll surface effected by the treatment to provide satin finish, an outstanding improvement in the efficiency of sugar juice extraction can be ensured.

circumferential grooves, an electrode spaced apart from said roll in facing relationship therewith'by a distance capable of effecting electrical discharge, means for providing water between said roll and said electrode, and an electric circuit,

the roll connected to the circuit as a cathode and the electrode connected to the circuit as an anode, whereby the circuit may effect repetitive discharges between the roll and the electrode to satin-finish the surface of said roll by the discharges.

2. The electrical discharge apparatus of claim 1 wherein said electrode is provided with spaced-apart projections conforming to the grooves in the roll and indentations conforming to the surface of the roll between the grooves.

3. The electrical discharge apparatus of claim 2 wherein said electrode is a turner plate.

4. The electrical discharge apparatus of claim 2 wherein said electrode is a scraper.

5. The electrical discharge apparatus of claim 1 including a water-retaining housing disposed about the electrode and spaced from the electrode whereby water from the waterproviding meansmay be retained in surrounding relationship with the electrode.

6. The electrical discharge apparatus of claim 5 including a holder supporting the electrode and the housing, means for advancing and retracting the holder toward and away from the roll generally perpendicularly to the axis of the roll, and means for moving the holder in a direction generally parallel to the axis of the roll.

7. An electrical discharge apparatus comprising a generally cylindrical sugar mill roll having a plurality of axially spaced circumferential grooves, an electrode spaced apart from the roll in facing relationship therewith by a distance capable of effecting electrical discharge, the electrode having spacedapart projections conforming to the grooves in the roll and in dentations conforming to the surface of the roll between the grooves, a nozzle adjacent the roll and the electrode for supplying water between the roll and the electrode, a holder supporting the electrode, a water-retaining housing supported by the holder surrounding the electrode and spaced therefrom whereby water may be retained in surrounding relationship with the electrode, means for advancing and retracting the holder toward and away from the ro generally perpendicularly to the axis of the roll, and means for moving the holder in a direction generally parallel to the axis of the roll. 

1. An electrical discharge apparatus comprising a generally cylindrical sugar mill roll having a plurality of axially spaced circumferential grooves, an electrode spaced apart from said roll in facing relationship therewith by a distance capable of effecting electrical discharge, means for providing water between said roll and said electrode, and an electric circuit, the roll connected to the circuit as a cathode and the electrode connected to the circuit as an anode, whereby the circuit may effect repetitive discharges between the roll and the electrode to satin-finish the surface of said roll by the discharges.
 2. The electrical discharge apparatus of claim 1 wherein said electrode is provided with spaced-apart projections conforming to the grooves in the roll and indentations conforming to the surface of the roll between the grooves.
 3. The electrical discharge apparatus of claim 2 wherein said electrode is a turner plate.
 4. The electrical discharge apparatus of claim 2 wherein said electrode is a scraper.
 5. The electrical discharge apparatus of claim 1 including a water-retaining housing disposed about the electrode and spaced from the electrode whereby water from the water-providing means may be retained in surrounding relationship with the electrode.
 6. The electrical discharge apparatus of claim 5 including a holder supporting the electrode and the housing, means for advancing and retracting the holder toward and awAy from the roll generally perpendicularly to the axis of the roll, and means for moving the holder in a direction generally parallel to the axis of the roll.
 7. An electrical discharge apparatus comprising a generally cylindrical sugar mill roll having a plurality of axially spaced circumferential grooves, an electrode spaced apart from the roll in facing relationship therewith by a distance capable of effecting electrical discharge, the electrode having spaced-apart projections conforming to the grooves in the roll and indentations conforming to the surface of the roll between the grooves, a nozzle adjacent the roll and the electrode for supplying water between the roll and the electrode, a holder supporting the electrode, a water-retaining housing supported by the holder surrounding the electrode and spaced therefrom whereby water may be retained in surrounding relationship with the electrode, means for advancing and retracting the holder toward and away from the ro generally perpendicularly to the axis of the roll, and means for moving the holder in a direction generally parallel to the axis of the roll. 